A known liquid ejection apparatus includes a line printer including a plurality of head units. Each of the head units is connected to a common fluid supply (e.g., a sub-tank). A pressure regulating valve is disposed between the fluid supply and the head units to maintain constant pressure in the respective head units. The pressure regulating valve is configured to open when a pressure differential across the valve becomes greater than a predetermined value. When a head unit ejects fluid, e.g., ink, an ink pressure in a chamber disposed downstream of the valve may be reduced, which may cause the pressure regulating valve to open. Accordingly, ink is supplied from the fluid supply.
Another known liquid ejection apparatus includes a negative pressure regulating unit between a fluid ejection head and a tank. The negative pressure regulating unit is configured to open and close in accordance with a pressure differential across the unit. The negative pressure regulating unit is configured to regulate or adjust an opening/closing pressure differential for opening/closing the unit. More specifically, the opening/closing pressure differential is altered by changing a load applied to a valve member with a weight placed on a movable plate that contacts a spring.